1. Field of the Invention
The field of the invention is industrial panel controls such as switches and indicator lights, and specifically adapters for use with such panel controls to permit their rapid connection to a prewired harness.
2. Background Art
Industrial panel controls include generally single and multiple contact switches and indicator lamps for use in the control of electrical equipment. Such panel controls are designed to resist the destructive effects of the industrial enviroment including temperature extremes and elevated levels of mechanical shock and vibration, and may include provisions for sealing the contacts and lamp elements against oil and water.
Ordinarily, such panel controls are wired to remote devices, such as contactors and a considerable length of wire may be required to connect the panel controls to such remote devices. In order to limit the voltage drop in the interconnecting wiring, panel controls ordinarily accommodate large gauge wire having low resistance per unit length. Connection to the wire is accomplished by means of screw terminals comprising conductive tabs with threaded holes for receiving specially engineered machine screws ("SEMS"). The exposed conductor of the wire is captured between the head of the SEMS and the conductive tab. Frequently, a saddle clamp, constructed of a C-shaped strip of metal will be held by the SEMS against the tab so as to further guide and restrain the wire being connected. Alternatively, a "crimp connector" having a pre-formed hook or loop may be attached to the exposed conductor of the wire and fastened to the tab by the SEMS. Another construction uses a "spade" connector attached to the conductor of the wire and pressed directly onto a corresponding conductive tab of the terminal and held by friction.
In complex control applications, the panel controls may be connected directly to an industrial controller. An industrial controller provides outputs and receives inputs, to and from various devices though input/output modules (I/O modules) communicating with the industrial controller via a high speed digital link. Inputs to the industrial controller may be from the contacts of a panel control while outputs of the industrial controller may be to the terminals of an indicator lamp of a panel control. A stored program executed by the industrial controller reads the inputs and changes the outputs in response to that program, as is generally understood in the art. The panel controls and the remote devices are connected to I/O modules and effectively communicate with each other via the industrial controller.
This use of an industrial controller to mediate between panel controls and remote electrical devices offers two advantages. First, the connections between the panel controls and the remote devices may be modified simply by reprogramming the industrial controller without the time consuming and expensive rewiring of the panel controls. Second, the I/O modules may be positioned near the panel controls and thus connected with short runs of low current wiring. Long runs of wiring between the panel controls and the remote devices are eliminated by the uses of remote I/O modules communicating with the industrial controller by high speed digital links.